Photolithographic methods

ABSTRACT

Provided are photoresist overcoat compositions, substrates coated with the overcoat compositions and methods of forming electronic devices by a negative tone development process. The compositions, coated substrates and methods find particular applicability in the manufacture of semiconductor devices.

This application claims the benefit of priority under 35 U.S.C. §119(e)to U.S. Provisional Application No. 61/533,106, filed Sep. 9, 2011, theentire contents of which are incorporated herein by reference.

The invention relates generally to the manufacture of electronicdevices. More specifically, this invention relates to photolithographicmethods which allow for the formation of fine patterns using a negativetone development process.

In the semiconductor manufacturing industry, photoresist materials areused for transferring an image to one or more underlying layers, such asmetal, semiconductor and dielectric layers, disposed on a semiconductorsubstrate, as well as to the substrate itself. To increase theintegration density of semiconductor devices and allow for the formationof structures having dimensions in the nanometer range, photoresists andphotolithography processing tools having high-resolution capabilitieshave been and continue to be developed.

Positive-tone chemically amplified photoresists are conventionally usedfor high-resolution processing. Such resists typically employ a resinhaving acid-labile leaving groups and a photoacid generator. Exposure toactinic radiation causes the acid generator to form an acid which,during post-exposure baking, causes cleavage of the acid-labile groupsin the resin. This creates a difference in solubility characteristicsbetween exposed and unexposed regions of the resist in an aqueousalkaline developer solution. Exposed regions of the resist are solublein the aqueous alkaline developer and are removed from the substratesurface, whereas unexposed regions, which are insoluble in thedeveloper, remain after development to form a positive image.

One approach to achieving nm-scale feature sizes in semiconductordevices is the use of short wavelengths of light, for example, 193 nm orless, during exposure of chemically amplified photoresists. To furtherimprove lithographic performance, immersion lithography tools have beendeveloped to effectively increase the numerical aperture (NA) of thelens of the imaging device, for example, a scanner having a KrF or ArFlight source. This is accomplished by use of a relatively highrefractive index fluid (i.e., an immersion fluid) between the lastsurface of the imaging device and the upper surface of the semiconductorwafer. The immersion fluid allows a greater amount of light to befocused into the resist layer than would occur with an air or inert gasmedium. When using water as the immersion fluid, the maximum numericalaperture can be increased, for example, from 1.2 to 1.35. With such anincrease in numerical aperture, it is possible to achieve a 40 nmhalf-pitch resolution in a single exposure process, thus allowing forimproved design shrink. This standard immersion lithography process,however, is generally not suitable for manufacture of devices requiringgreater resolution, for example, for the 32 nm and 22 nm half-pitchnodes.

Considerable effort has been made to extend the practical resolutionbeyond that achieved with positive tone development from both amaterials and processing standpoint. One such example involves negativetone development (NTD) of a traditionally positive-type chemicallyamplified photoresist. The NTD process allows for improved resolutionand process window as compared with standard positive tone imaging bymaking use of the superior imaging quality obtained with bright fieldmasks for printing critical dark field layers. NTD resists typicallyemploy a resin having acid-labile (or acid-cleavable) groups and aphotoacid generator. Exposure to actinic radiation causes the photoacidgenerator to form an acid which, during post-exposure baking, causescleavage of the acid-labile groups giving rise to a polarity switch inthe exposed regions. As a result, a difference in solubilitycharacteristics is created between exposed and unexposed regions of theresist such that unexposed regions of the resist can be removed byorganic developers such as ketones, esters or ethers, leaving behind apattern created by the insoluble exposed regions.

The use in immersion lithography of a protective barrier materialbetween the photoresist and immersion fluid to avoid leaching ofphotoresist components and fouling of the exposure tool optics, as wellas providing antireflective properties, is known. The barrier layer canbe formed from components added to the photoresist composition whichself-segregate to the resist layer upper surface during the spin-coatingprocess. Alternatively, a composition separate from the photoresist canbe used to form an overcoat or topcoat layer over the photoresist layer.U.S. Patent Application Pub. No. US2011/0020755A1 discloses an NTDmethod which involves formation of a protective film on a resist filmbefore exposing the resist film, exposing the resist film via animmersion medium and performing development with a negative developer.The protective film composition contains a solvent for even applicationof the protective film to the top of the resist film without dissolvingthe resist film, a resin having no aromatic groups having transparencyto 193 nm light and optionally a surfactant.

It has been observed by the inventors that “necking” of contact holes or“T-topping” in line and trench patterns can occur in the developedresist patterns resulting from the NTD process. This effect isillustrated in FIG. 1 in the case of contact hole pattern formation. Asubstrate 100 coated with one or more layers to be patterned 102, aphotoresist layer 104 and an immersion topcoat layer 106. Thephotoresist layer is exposed to activating radiation 108 through aphotomask 110 to create a difference in solubility between exposed andunexposed regions as shown in FIG. 1A. The photomask has opticallytransparent and optically opaque regions 112, 114 corresponding toregions of the resist layer to remain and be removed, respectively, in asubsequent development step. Following post exposure bake (PEB), alatent image, defined by the boundary (dashed line 116) betweenpolarity-switched and unswitched regions, is formed in the photoresistas shown in FIG. 1B. The polarity-switch undesirably extends intoregions 118 at the resist surface which, during the exposure step, laidbeneath the opaque mask pattern 114. This is believed to be a result ofthe diffusion of stray light beneath edges of the photomask opaquepattern. During development with an organic developer, the topcoat layer106 and unexposed (unswitched) regions of the photoresist layer 104 areremoved to form contact hole pattern 120, as shown in FIG. 1C. Theresulting pattern exhibits necking at the resist layer upper surfacewhere the polarity-switched resist regions 118 are not removed. Theoccurrence of “necking” or “T-topping” generally results in a poorprocess window such as depth of focus and exposure latitude. Theseproblems can lead, for example, to random missing contact holes or tomicro-bridging defects in the case of narrow trench or line patternformation, thereby adversely impacting device yield. The aforementionedUS2011/0020755A1 document does not recognize the problem of T-topping ornecking in formed resist patterns or a solution thereto.

There is a continuing need in the art for improved photolithographicmethods for negative tone development which allow for the formation offine patterns in electronic device fabrication and which avoid orconspicuously ameliorate one or more of the foregoing problemsassociated with the state of the art. In accordance with an aspect ofthe invention, methods of forming electronic devices are provided. Themethods comprise: (a) providing a semiconductor substrate comprising oneor more layers to be patterned; (b) forming a photoresist layer over theone or more layers to be patterned; (c) coating a photoresist overcoatcomposition over the photoresist layer, wherein the overcoat compositioncomprises a basic quencher, a polymer and an organic solvent; (d)exposing the layer to actinic radiation; and (e) developing the exposedfilm with an organic solvent developer.

Also provided are electronic devices formed by the methods describedherein.

As used herein: “g” means grams; wt % means weight percent; “L” meansliter; “mL” means milliliter; “nm” means nanometer; “mm” meansmillimeter; “min” means minute; “h” means hour; “A” means Angstrom; “mol%” means mole percent; “Mw” means weight average molecular weight; and“Mn” means number average molecular weight; “PDI” means polydispersityindex=Mw/Mn; “copolymer” is inclusive of polymers containing two or moredifferent types of polymerized units; “alkyl” is inclusive of linear,branched and cyclic alkyl structures; “aliphatic” is inclusive oflinear, branched and cyclic aliphatic structures; and the articles “a”and “an” are inclusive of one or more.

The present invention will be described with reference to the followingdrawings, in which like reference numerals denote like features, and inwhich:

FIG. 1A-C illustrates a contact hole formation process according to therelated art; and

FIG. 2A-C illustrates a process flow for forming a photolithographicpattern in accordance with the invention.

PHOTORESIST OVERCOAT COMPOSITIONS

The compositions useful in the invention when coated over a photoresistlayer in a negative tone development process can provide variousbenefits, such as one or more of geometrically uniform resist patterns,reduced reflectivity during resist exposure, improved focus latitude,improved exposure latitude and reduced defectivity. These benefits canbe achieved when using the compositions in dry lithography or immersionlithography processes. When used in immersion lithography, the overcoatcompositions can be used to form an effective barrier layer foravoidance of leaching of photoresist components into the immersion fluidand to provide desirable contact angle characteristics with theimmersion fluid to allow for increased exposure scan speeds.

The photoresist overcoat compositions include a basic quencher, apolymer, an organic solvent and can include additional optionalcomponents. The overcoat compositions include a polymer which imparts tolayers formed from the compositions beneficial barrier properties tominimize or prevent migration of photoresist components into theimmersion fluid, and beneficial contact angle characteristics to providefor a high immersion fluid receding contact angle at theovercoat/immersion fluid interface, thereby allowing for faster exposuretool scanning speeds. A layer of the overcoat composition in a driedstate typically has a water receding contact angle of from 70° to 85°,preferably from 75 to 80°. The phrase “in a dried state” meanscontaining 8 wt % or less of solvent, based on the entire composition.

The polymer should have very good developability before and afterphotolithographic treatment. To minimize residue defects originated fromthe overcoat materials, the dissolution rate of a dried layer of theovercoat composition should be greater than that of the underlyingphotoresist layer in the developer used in the patterning process. Thepolymer typically exhibits a developer dissolution rate of 100 Å/secondor higher, preferably 1000 Å/second or higher. The polymer can be freeof silicon and fluorine. The polymer is soluble in the organic solventof the overcoat composition, described herein, and is soluble in organicdevelopers used in negative tone development processes. The polymerpreferably has a low surface energy relative to the basic quencherdescribed below.

The polymer is preferably formed from a monomer having the followinggeneral formula (I):

wherein: R₁ is chosen from hydrogen and substituted or unsubstituted C1to C3 alkyl, preferably hydrogen or methyl; R₂ is chosen fromsubstituted and unsubstituted C1 to C15 alkyl, preferably C4 to C8alkyl, more preferably C4 to C6 alkyl, the substituted alkyls including,for example, haloalkyl and haloalcohol such as fluoroalkyl andfluoroalcohol, and is preferably branched to provide higher recedingcontact angles; X is oxygen, sulfur or is represented by the formulaNR₃, wherein R₃ is chosen from hydrogen and substituted andunsubstituted C1 to C10 alkyl, preferably C1 to C5 alkyl; and Z is asingle bond or a spacer unit chosen from substituted and unsubstitutedaliphatic (such as C1 to C6 alkylene) and aromatic hydrocarbons, andcombinations thereof, optionally with one or more linking moiety chosenfrom —O—, —S—, —COO— and —CONR₄— wherein R₄ is chosen from hydrogen andsubstituted and unsubstituted C1 to C10 alkyl, preferably C2 to C6,alkyl.

Exemplary suitable monomers of general formula (I) are described below,but are not limited to these structures. For purposes of thesestructures, “R₁” and “X” are as defined above.

The monomer of general formula (I) is preferably of the followinggeneral formula (II):

wherein R₁ and Z are as defined above, and R₅, R₆, and R₇ independentlyrepresent hydrogen or a C₁ to C₃ alkyl, fluoroalkyl or fluoroalcoholgroup. Suitable monomers of general formula (II) are described among theabove-exemplified structures.

The content of the polymer may depend, for example, on whether thelithography is a dry or immersion-type process. For example, the polymerlower limit for immersion lithography is generally dictated by the needto prevent leaching of the resist components. A higher polymer contentwill typically result in pattern degradation. The polymer is typicallypresent in the compositions in an amount of from 80 to 99 wt %, moretypically from 90 to 98 wt %, based on total solids of the overcoatcomposition. The weight average molecular weight of the polymer istypically less than 400,000, preferably from 5000 to 50,000, morepreferably from 5000 to 25,000.

Polymers useful in the overcoat compositions can be homopolymers formedfrom the monomers of general formula (I) or can be copolymers having aplurality of distinct repeat units, for example, two, three or fourdistinct repeat units. The distinct units can, for example, includepolymerized units of different monomers of general formula (I).Exemplary copolymers useful in the overcoat compositions as the polymerinclude the following copolymers:

The overcoat compositions typically include a single polymer, but canoptionally include one or more additional polymer of general formula (I)or other polymer. Suitable polymers and monomers for use in the overcoatcompositions are commercially available and/or can readily be made bypersons skilled in the art.

The overcoat compositions further include an organic solvent or mixtureof organic solvents. Suitable solvent materials to formulate and castthe overcoat composition exhibit excellent solubility characteristicswith respect to the non-solvent components of the overcoat composition,but do not appreciably dissolve an underlying photoresist layer.Suitable organic solvents for the overcoat composition include, forexample: alkyl esters such as alkyl propionates such as n-butylpropionate, n-pentyl propionate, n-hexyl propionate and n-heptylpropionate, and alkyl butyrates such as n-butyl butyrate, isobutylbutyrate and isobutyl isobutyrate; ketones such as2,5-dimethyl-4-hexanone and 2,6-dimethyl-4-heptanone; aliphatichydrocarbons such as n-heptane, n-nonane, n-octane, n-decane,2-methylheptane, 3-methylheptane, 3,3-dimethylhexane and2,3,4-trimethylpentane, and fluorinated aliphatic hydrocarbons such asperfluoroheptane; and alcohols such as straight, branched or cyclicC₄-C₉ monohydric alcohol such as 1-butanol, 2-butanol,3-methyl-1-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol,2-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 2-hexanol, 2-heptanol,2-octanol, 3-hexanol, 3-heptanol, 3-octanol and 4-octanol;2,2,3,3,4,4-hexafluoro-1-butanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanoland 2,2,3,3,4,4,5,5,6,6-decafluoro-1-hexanol, and C₅-C₉ fluorinateddiols such as 2,2,3,3,4,4-hexafluoro-1,5-pentanediol,2,2,3,3,4,4,5,5-octafluoro-1,6-hexanediol and2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1,8-octanediol; and mixturescontaining one or more of these solvents. Of these organic solvents,alkyl propionates, alkyl butyrates and ketones, preferably branchedketones, are preferred and, more preferably, C₈-C₉ alkyl propionates,C₈-C₉ alkyl propionates, C₈-C₉ ketones, and mixtures containing one ormore of these solvents. Suitable mixed solvents include, for example,mixtures of an alkyl ketone and an alkyl propionate such as the alkylketones and alkyl propionates described above. The solvent component ofthe overcoat composition is typically present in an amount of from 90 to99 wt % based on the overcoat composition.

The photoresist overcoat compositions further include a basic quencher.The basic quencher is present for purposes of neutralizing acidgenerated in the surface region of the underlying photoresist layer bystray light which reaches what are intended to be unexposed (dark)regions of the photoresist layer. This allows for improvement in depthof focus in the defocus area and exposure latitude by controllingunwanted deprotection reaction in the unexposed areas. As a result,irregularities in the profile, for example, necking and T-topping, informed resist patterns can be minimized or avoided.

To allow for effective interaction between the basic quencher and theacid generated in the dark areas of the underlying photoresist layer,the basic quencher should be of a non-surfactant-type. That is, thebasic quencher should not be of a type that migrates to the top surfaceof the overcoat layer due, for example, to a low surface free energyrelative to other components of the overcoat composition. In such acase, the basic quencher would not be appreciably present at thephotoresist layer interface for interaction with the generated acid toprevent acid deprotection. The basic quencher should therefore be of atype that is present at the overcoat layer/photoresist layer interface,whether being uniformly dispersed through the overcoat layer or forminga graded or segregated layer at the interface. Such a segregated layercan be achieved by selection of a basic quencher having a high surfacefree energy relative to other components of the overcoat composition.

Suitable basic quenchers include, for example: linear and cyclic amidesand derivatives thereof such as N,N-bis(2-hydroxyethyl)pivalamide,N,N-Diethylacetamide, N1,N1,N3,N3-tetrabutylmalonamide,1-methylazepan-2-one, 1-allylazepan-2-one and tert-butyl1,3-dihydroxy-2-(hydroxymethyl)propan-2-ylcarbamate; aromatic aminessuch as pyridine, and di-tert-butyl pyridine; aliphatic amines such astriisopropanolamine, n-tert-butyldiethanolamine,tris(2-acetoxy-ethyl)amine,2,2′,2″,2′″-(ethane-1,2-diylbis(azanetriyl))tetraethanol, and2-(dibutylamino)ethanol, 2,2′,2″-nitrilotriethanol; cyclic aliphaticamines such as 1-(tert-butoxycarbonyl)-4-hydroxypiperidine, tert-butyl1-pyrrolidinecarboxylate, tert-butyl 2-ethyl-1H-imidazole-1-carboxylate,di-tert-butyl piperazine-1,4-dicarboxylate and N(2-acetoxy-ethyl)morpholine. Of these basic quenchers,1-(tert-butoxycarbonyl)-4-hydroxypiperidine and triisopropanolamine arepreferred. While the content of the basic quencher will depend, forexample, on the content of the photoacid generator in the underlyingphotoresist layer, it is typically present in an amount of from 0.1 to 5wt %, preferably from 0.5 to 3 wt %, more preferably from 1 to 3 wt %,based on total solids of the overcoat composition.

The photoresist overcoat compositions can include one or more optionalmaterials. For example, the compositions can include one or more ofactinic and contrast dyes, anti-striation agents, and the like. Ofthese, actinic and contrast dyes are preferred for enhancingantireflective properties of layers formed from the compositions. Suchoptional additives if used are typically present in the composition inminor amounts such as from 0.1 to 10 wt % based on total solids of theovercoat composition. The overcoat compositions are preferably free ofacid generator compounds, for example, thermal acid generator compoundsand photoacid generator compounds, as such compounds may neutralize theeffect of the basic quencher in the overcoat compositions.

The photoresist overcoat compositions can be prepared following knownprocedures. For example, the compositions can be prepared by dissolvingsolid components of the composition in the solvent components. Thedesired total solids content of the compositions will depend on factorssuch as the particular polymer(s) in the composition and desired finallayer thickness. Preferably, the solids content of the overcoatcompositions is from 1 to 10 wt %, more preferably from 1 to 5 wt %,based on the total weight of the composition.

Resist overcoat layers formed from the compositions typically have anindex of refraction of 1.4 or greater at 193 nm, preferably 1.47 orgreater at 193 nm The index of refraction can be tuned by changing thecomposition of the polymer(s) or other components of the overcoatcomposition. For example, increasing the relative amount of organiccontent in the overcoat composition may provide increased refractiveindex of the layer. Preferred overcoat composition layers will have arefractive index between that of the immersion fluid and the photoresistat the target exposure wavelength.

Reflectivity of the overcoat layer can be reduced if the refractiveindex of the overcoat layer (n₁) is the geometric mean of that of thematerials on either side (n₁=√(n₀ n₂)), where n₀ is the refractive indexof water in the case of immersion lithography or air for drylithography, and n₂ is the refractive index of the photoresist. Also toenhance antireflective properties of layers formed from the overcoatcompositions, it is preferred that the thickness of the overcoat (d₁) ischosen such that the wavelength in the overcoat is one quarter thewavelength of the incoming wave (λ₀). For a quarter wavelengthantireflective coating of an overcoat composition with a refractiveindex n₁, the thickness d₁ that gives minimum reflection is calculatedby d₁=λ₀/(4 n₁).

Photoresist Compositions

Photoresist compositions useful in the invention includechemically-amplified photoresist compositions comprising a matrixpolymer that is acid-sensitive, meaning that as part of a layer of thephotoresist composition, the polymer and composition layer undergo achange in solubility in an organic developer as a result of reactionwith acid generated by a photoacid generator following softbake,exposure to activating radiation and post exposure bake. The change insolubility is brought about when acid-labile groups such asphotoacid-labile ester or acetal groups in the matrix polymer undergo aphotoacid-promoted deprotection reaction on exposure to activatingradiation and heat treatment. Suitable photoresist compositions usefulfor the invention are commercially available

For imaging at sub-200 nm wavelengths such as 193 nm, the matrix polymeris typically substantially free (e.g., less than 15 mole %) of phenyl,benzyl or other aromatic groups where such groups are highly absorbingof the radiation. Suitable polymers that are substantially or completelyfree of aromatic groups are disclosed in European application EP930542A1and U.S. Pat. Nos. 6,692,888 and 6,680,159, all of the Shipley Company.Preferable acid labile groups include, for example, acetal groups orester groups that contain a tertiary non-cyclic alkyl carbon (e.g.,t-butyl) or a tertiary alicyclic carbon (e.g., methyladamantyl)covalently linked to a carboxyl oxygen of an ester of the matrixpolymer.

Suitable matrix polymers further include polymers that contain(alkyl)acrylate units, preferably including acid-labile(alkyl)acrylateunits, such as t-butyl acrylate, t-butyl methacrylate, methyladamantylacrylate, methyl adamantyl methacrylate, ethylfenchyl acrylate,ethylfenchyl methacrylate, and the like, and other non-cyclic alkyl andalicyclic(alkyl)acrylates. Such polymers have been described, forexample, in U.S. Pat. No. 6,057,083, European Published ApplicationsEP01008913A1 and EP00930542A1, and U.S. Pat. No. 6,136,501.

Other suitable matrix polymers include, for example, those which containpolymerized units of a non-aromatic cyclic olefin (endocyclic doublebond) such as an optionally substituted norbornene, for example,polymers described in U.S. Pat. Nos. 5,843,624 and 6, 048,664.

Still other suitable matrix polymers include polymers that containpolymerized anhydride units, particularly polymerized maleic anhydrideand/or itaconic anhydride units, such as disclosed in European PublishedApplication EP01008913A1 and U.S. Pat. No. 6,048,662.

Also suitable as the matrix polymer is a resin that contains repeatunits that contain a hetero atom, particularly oxygen and/or sulfur (butother than an anhydride, i.e., the unit does not contain a keto ringatom). The heteroalicyclic unit can be fused to the polymer backbone,and can comprise a fused carbon alicyclic unit such as provided bypolymerization of a norbornene group and/or an anhydride unit such asprovided by polymerization of a maleic anhydride or itaconic anhydride.Such polymers are disclosed in PCT/US01/14914 and U.S. Pat. No.6,306,554. Other suitable hetero-atom group containing matrix polymersinclude polymers that contain polymerized carbocyclic aryl unitssubstituted with one or more hetero-atom (e.g., oxygen or sulfur)containing groups, for example, hydroxy naphthyl groups, such asdisclosed in U.S. Pat. No. 7,244,542.

Blends of two or more of the above-described matrix polymers cansuitably be used in the photoresist compositions.

Suitable matrix polymers for use in the photoresist compositions arecommercially available and can readily be made by persons skilled in theart. The matrix polymer is present in the resist composition in anamount sufficient to render an exposed coating layer of the resistdevelopable in a suitable developer solution. Typically, the matrixpolymer is present in the composition in an amount of from 50 to 95 wt %based on total solids of the resist composition. The weight averagemolecular weight M_(w) of the matrix polymer is typically less than100,000, for example, from 5000 to 100,000, more typically from 5000 to15,000.

The photosensitive composition further comprises a photoactive componentsuch as a a photoacid generator (PAG) employed in an amount sufficientto generate a latent image in a coating layer of the composition uponexposure to activating radiation. For example, the photoacid generatorwill suitably be present in an amount of from about 1 to 20 wt % basedon total solids of the photoresist composition. Typically, lesseramounts of the PAG will be suitable for chemically amplified resists ascompared with non-chemically amplified materials.

Suitable PAGs are known in the art of chemically amplified photoresistsand include, for example: onium salts, for example, triphenylsulfoniumtrifluoromethanesulfonate, (p-tert-butoxyphenyl)diphenylsulfoniumtrifluoromethanesulfonate, tris(p-tert-butoxyphenyl)sulfoniumtrifluoromethanesulfonate, triphenylsulfonium p-toluenesulfonate;nitrobenzyl derivatives, for example, 2-nitrobenzyl-p-toluenesulfonate,2,6-dinitrobenzyl-p-toluenesulfonate, and2,4-dinitrobenzyl-p-toluenesulfonate; sulfonic acid esters, for example,1,2,3-tris(methanesulfonyloxy)benzene,1,2,3-tris(trifluoromethanesulfonyloxy)benzene, and1,2,3-tris(p-toluenesulfonyloxy)benzene; diazomethane derivatives, forexample, bis(benzenesulfonyl)diazomethane,bis(p-toluenesulfonyl)diazomethane; glyoxime derivatives, for example,bis-O-(p-toluenesulfonyl)-α-dimethylglyoxime, andbis-O-(n-butanesulfonyl)-α-dimethylglyoxime; sulfonic acid esterderivatives of an N-hydroxyimide compound, for example,N-hydroxysuccinimide methanesulfonic acid ester, N-hydroxysuccinimidetrifluoromethanesulfonic acid ester; and halogen-containing triazinecompounds, for example,2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine, and2-(4-methoxynaphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine. One ormore of such PAGs can be used.

Suitable solvents for the photoresist compositions include, for example:glycol ethers such as 2-methoxyethyl ether (diglyme), ethylene glycolmonomethyl ether, and propylene glycol monomethyl ether; propyleneglycol monomethyl ether acetate; lactates such as methyl lactate andethyl lactate; propionates such as methyl propionate, ethyl propionate,ethyl ethoxy propionate and methyl-2-hydroxy isobutyrate; Cellosolveesters such as methyl Cellosolve acetate; aromatic hydrocarbons such astoluene and xylene; and ketones such as acetone, methylethyl ketone,cyclohexanone and 2-heptanone. A blend of solvents such as a blend oftwo, three or more of the solvents described above also are suitable.The solvent is typically present in the composition in an amount of from90 to 99 wt %, more typically from 95 to 98 wt %, based on the totalweight of the photoresist composition.

The photoresist compositions can further include other optionalmaterials. For example, negative-acting resist compositions typicallyalso include a crosslinker component. Suitable crosslinker componentsinclude, for example, an amine-based material such as a melamine resin,that will cure, crosslink or harden upon exposure to acid on exposure ofa photoacid generator to activating radiation. Preferred crosslinkersinclude amine-based materials, including melamine, glycolurils,benzoguanamine-based materials and urea-based materials.Melamine-formaldehyde resins are generally most preferred. Suchcrosslinkers are commercially available, e.g. the melamine resins soldby American Cyanamid under the trade names Cymel 300, 301 and 303.Glycoluril resins are sold by American Cyanamid under trade names Cymel1170, 1171, 1172, urea-based resins are sold under the trade names ofBeetle 60, 65 and 80, and benzoguanamine resins are sold under the tradenames Cymel 1123 and 1125. For imaging at sub-200 nm wavelengths such as193 nm, preferred negative-acting photoresists are disclosed in WO03077029 to the Shipley Company.

The photoresist compositions can also include other optional materials.For example, the compositions can include one or more of actinic andcontrast dyes, anti-striation agents, plasticizers, speed enhancers,sensitizers, and the like. Such optional additives if used are typicallypresent in the composition in minor amounts such as from 0.1 to 10 wt %based on total solids of the photoresist composition.

A preferred optional additive of the resist compositions is an addedbase. Suitable bases are described above with respect to the basicquencher in the overcoat composition. The added base is suitably used inrelatively small amounts, for example, from 0.01 to 5 wt %, preferablyfrom 0.1 to 2 wt %, based on total solids of the photoresistcomposition.

The photoresists can be prepared following known procedures. Forexample, the resists can be prepared as coating compositions bydissolving the components of the photoresist in a suitable solvent, forexample, one or more of: a glycol ether such as 2-methoxyethyl ether(diglyme), ethylene glycol monomethyl ether, propylene glycol monomethylether; propylene glycol monomethyl ether acetate; lactates such as ethyllactate or methyl lactate, with ethyl lactate being preferred;propionates, particularly methyl propionate, ethyl propionate and ethylethoxy propionate; a Cellosolve ester such as methyl Cellosolve acetate;an aromatic hydrocarbon such toluene or xylene; or a ketone such asmethylethyl ketone, cyclohexanone and 2-heptanone. The desired totalsolids content of the photoresist will depend on factors such as theparticular polymers in the composition, final layer thickness andexposure wavelength. Typically the solids content of the photoresistvaries from 1 to 10 wt %, more typically from 2 to 5 wt %, based on thetotal weight of the photoresist composition.

Negative Tone Development Methods

Processes in accordance with the invention will now be described withreference to FIG. 2A-C, which illustrates an exemplary process flow forforming a photolithographic pattern by negative tone development.

FIG. 2A depicts in cross-section a substrate 100 which may includevarious layers and features. The substrate can be of a material such asa semiconductor, such as silicon or a compound semiconductor (e.g.,III-V or II-VI), glass, quartz, ceramic, copper and the like. Typically,the substrate is a semiconductor wafer, such as single crystal siliconor compound semiconductor wafer, and may have one or more layers andpatterned features formed on a surface thereof. One or more layers to bepatterned 102 may be provided over the substrate 100. Optionally, theunderlying base substrate material itself may be patterned, for example,when it is desired to form trenches in the substrate material. In thecase of patterning the base substrate material itself, the pattern shallbe considered to be formed in a layer of the substrate.

The layers may include, for example, one or more conductive layers suchas layers of aluminum, copper, molybdenum, tantalum, titanium, tungsten,alloys, nitrides or silicides of such metals, doped amorphous silicon ordoped polysilicon, one or more dielectric layers such as layers ofsilicon oxide, silicon nitride, silicon oxynitride, or metal oxides,semiconductor layers, such as single-crystal silicon, and combinationsthereof. The layers to be etched can be formed by various techniques,for example, chemical vapor deposition (CVD) such as plasma-enhancedCVD, low-pressure CVD or epitaxial growth, physical vapor deposition(PVD) such as sputtering or evaporation, or electroplating. Theparticular thickness of the one or more layers to be etched 102 willvary depending on the materials and particular devices being formed.

Depending on the particular layers to be etched, film thicknesses andphotolithographic materials and process to be used, it may be desired todispose over the layers 102 a hard mask layer and/or a bottomantireflective coating (BARC) over which a photoresist layer 104 is tobe coated. Use of a hard mask layer may be desired, for example, withvery thin resist layers, where the layers to be etched require asignificant etching depth, and/or where the particular etchant has poorresist selectivity. Where a hard mask layer is used, the resist patternsto be formed can be transferred to the hard mask layer which, in turn,can be used as a mask for etching the underlying layers 102. Suitablehard mask materials and formation methods are known in the art. Typicalmaterials include, for example, tungsten, titanium, titanium nitride,titanium oxide, zirconium oxide, aluminum oxide, aluminum oxynitride,hafnium oxide, amorphous carbon, silicon oxynitride and silicon nitride.The hard mask layer can include a single layer or a plurality of layersof different materials. The hard mask layer can be formed, for example,by chemical or physical vapor deposition techniques.

A bottom antireflective coating may be desirable where the substrateand/or underlying layers would otherwise reflect a significant amount ofincident radiation during photoresist exposure such that the quality ofthe formed pattern would be adversely affected. Such coatings canimprove depth-of-focus, exposure latitude, linewidth uniformity and CDcontrol. Antireflective coatings are typically used where the resist isexposed to deep ultraviolet light (300 nm or less), for example, KrFexcimer laser light (248 nm) or ArF excimer laser light (193 nm). Theantireflective coating can comprise a single layer or a plurality ofdifferent layers. Suitable antireflective materials and methods offormation are known in the art. Antireflective materials arecommercially available, for example, those sold under the AR™ trademarkby Rohm and Haas Electronic Materials LLC (Marlborough, Mass. USA), suchas AR™40A and AR™124 antireflectant materials.

A photoresist layer 104 formed from a composition such as describedherein is disposed on the substrate over the antireflective layer (ifpresent). The photoresist composition can be applied to the substrate byspin-coating, dipping, roller-coating or other conventional coatingtechnique. Of these, spin-coating is typical. For spin-coating, thesolids content of the coating solution can be adjusted to provide adesired film thickness based upon the specific coating equipmentutilized, the viscosity of the solution, the speed of the coating tooland the amount of time allowed for spinning. A typical thickness for thephotoresist layer 104 is from about 500 to 3000 Å.

The photoresist layer can next be softbaked to minimize the solventcontent in the layer, thereby forming a tack-free coating and improvingadhesion of the layer to the substrate. The softbake can be conducted ona hotplate or in an oven, with a hotplate being typical. The softbaketemperature and time will depend, for example, on the particularmaterial of the photoresist and thickness. Typical softbakes areconducted at a temperature of from about 90 to 150° C., and a time offrom about 30 to 90 seconds.

A photoresist overcoat layer 206 formed from an overcoat composition asdescribed herein is formed over the photoresist layer 104. The overcoatcomposition is typically applied to the substrate by spin-coating. Thesolids content of the coating solution can be adjusted to provide adesired film thickness based upon the specific coating equipmentutilized, the viscosity of the solution, the speed of the coating tooland the amount of time allowed for spinning. To reduce reflectivity ofthe overcoat layer, the thickness is preferably chosen such that thewavelength in the overcoat is one quarter the wavelength of the incomingwave. A typical thickness for the photoresist overcoat layer 206 is from200 to 1000 Å.

The photoresist overcoat layer can next be baked to remove minimize thesolvent content in the layer. The bake can be conducted on a hotplate orin an oven, with a hotplate being typical. Typical bakes are conductedat a temperature of from about 80 to 120° C., and a time of from about30 to 90 seconds. The basic quencher may be present in the overcoatlayer 206 dispersed homogeneously through the overcoat layer, or may bepresent as a segregated or graded quencher region 207.

The photoresist layer 104 is next exposed to activating radiation 108through a first photomask 110 to create a difference in solubilitybetween exposed and unexposed regions. References herein to exposing aphotoresist composition to radiation that is activating for thecomposition indicates that the radiation is capable of forming a latentimage in the photoresist composition. The photomask has opticallytransparent and optically opaque regions 112, 114 corresponding toregions of the resist layer to remain and be removed, respectively, in asubsequent development step. The exposure wavelength is typicallysub-400 nm, sub-300 nm or sub-200 nm, with 248 nm and 193 nm beingtypical. The methods find use in immersion or dry (non-immersion)lithography techniques. The exposure energy is typically from about 10to 80 mJ/cm², dependent upon the exposure tool and the components of thephotosensitive composition.

Following exposure of the photoresist layer 104, a post-exposure bake(PEB) is performed. The PEB can be conducted, for example, on a hotplateor in an oven. Conditions for the PEB will depend, for example, on theparticular photoresist composition and layer thickness. The PEB istypically conducted at a temperature of from about 80 to 150° C., and atime of from about 30 to 90 seconds. Following post exposure bake, it isbelieved that the basic quencher diffuses into the surface region of thephotoresist layer 104 as shown by dashed lines 209. A latent image 216defined by the boundary (dashed line) between polarity-switched andunswitched regions (corresponding to exposed and unexposed regions,respectively) is formed in the photoresist as shown in FIG. 2B. Thediffused basic quencher in the photoresist is believed to preventpolarity switch in undesired dark regions of the photoresist layer,resulting in a latent image with vertical walls.

The overcoat layer 206 and exposed photoresist layer are next developedto remove unexposed regions of the photoresist layer 104, leavingexposed regions forming an open resist pattern 104′ with contact holepattern 220 having vertical sidewalls as shown in FIG. 2C. The developeris typically an organic developer, for example, a solvent chosen fromketones, esters, ethers, hydrocarbons, and mixtures thereof. Suitableketone solvents include, for example, acetone, 2-hexanone,5-methyl-2-hexanone, 2-heptanone, 4-heptanone, 1-octanone, 2-octanone,1-nonanone, 2-nonanone, diisobutyl ketone, cyclohexanone,methylcyclohexanone, phenylacetone, methyl ethyl ketone and methylisobutyl ketone. Suitable ester solvents include, for example, methylacetate, butyl acetate, ethyl acetate, isopropyl acetate, amyl acetate,propylene glycol monomethyl ether acetate, ethylene glycol monoethylether acetate, diethylene glycol monobutyl ether acetate, diethyleneglycol monoethyl ether acetate, ethyl-3-ethoxypropionate, 3-methoxybutylacetate, 3-methyl-3-methoxybutyl acetate, methyl formate, ethyl formate,butyl formate, propyl formate, ethyl lactate, butyl lactate and propyllactate. Suitable ether solvents include, for example, dioxane,tetrahydrofuran and glycol ether solvents, for example, ethylene glycolmonomethyl ether, propylene glycol monomethyl ether, ethylene glycolmonoethyl ether, propylene glycol monoethyl ether, diethylene glycolmonomethyl ether, triethylene glycol monoethyl ether and methoxymethylbutanol. Suitable amide solvents include, for example,N-methyl-2-pyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamideSuitable hydrocarbon solvents include, for example, aromatic hydrocarbonsolvents such as toluene and xylene. In addition, mixtures of thesesolvents, or one or more of the listed solvents mixed with a solventother than those described above or mixed with water can be used. Othersuitable solvents include those used in the photoresist composition. Thedeveloper is preferably 2-heptanone or a butyl acetate such as n-butylacetate.

Mixtures of organic solvents can preferably be employed as a developer,for example, a mixture of a first and second organic solvent. The firstorganic solvent can be chosen from hydroxy alkyl esters such asmethyl-2-hydroxyisobutyrate and ethyl lactate; and linear or branched C₅to C₆ alkoxy alkyl acetates such as propylene glycol monomethyl etheracetate (PGMEA). Of the first organic solvents, 2-heptanone and5-methyl-2-hexanone are preferred. The second organic solvent can bechosen from linear or branched unsubstituted C₆ to C₈ alkyl esters suchas n-butyl acetate, n-pentyl acetate, n-butyl propionate, n-hexylacetate, n-butyl butyrate and isobutyl butyrate; and linear or branchedC₈ to C₉ ketones such as 4-octanone, 2,5-dimethyl-4-hexanone and2,6-dimethyl-4-heptanone. Of the second organic solvents, n-butylacetate, n-butyl propionate and 2,6-dimethyl-4-heptanone are preferred.Preferred combinations of the first and second organic solvent include2-heptanone/n-butyl propionate, cyclohexanone/n-butyl propionate,PGMEA/n-butyl propionate, 5-methyl-2-hexanone/n-butyl propionate,2-heptanone/2,6-dimethyl-4-heptanone and 2-heptanone/n-butyl acetate. Ofthese, 2-heptanone/n-butyl acetate and 2-heptanone/n-butyl propionateare particularly preferred.

The organic solvents are typically present in the developer in acombined amount of from 90 wt % to 100 wt %, more typically greater than95 wt %, greater than 98 wt %, greater than 99 wt % or 100 wt %, basedon the total weight of the developer.

The developer material may include optional additives, for example,surfactants such as described above with respect to the photoresist.Such optional additives typically will be present in minorconcentrations, for example, in amounts of from about 0.01 to 5 wt %based on the total weight of the developer.

The developer can be applied to the substrate by known techniques, forexample, by spin-coating or puddle-coating. The development time is fora period effective to remove the unexposed regions of the photoresist,with a time of from 5 to 30 seconds being typical. Development istypically conducted at room temperature. The development process can beconducted without use of a cleaning rinse following development. In thisregard, it has been found that the development process can result in aresidue-free wafer surface rendering such extra rinse step unnecessary.

The BARC layer, if present, is selectively etched using resist pattern104′ as an etch mask, exposing the underlying hardmask layer. Thehardmask layer is next selectively etched, again using the resistpattern 104′ as an etch mask, resulting in patterned BARC and hardmasklayers. Suitable etching techniques and chemistries for etching the BARClayer and hardmask layer are known in the art and will depend, forexample, on the particular materials of these layers. Dry-etchingprocesses such as reactive ion etching are typical. The resist pattern104′ and patterned BARC layer are next removed from the substrate usingknown techniques, for example, oxygen plasma ashing.

Using the hardmask pattern as an etch mask, the one or more layers 102are selectively etched. Suitable etching techniques and chemistries foretching the underlying layers 102 are known in the art, with dry-etchingprocesses such as reactive ion etching being typical. The patternedhardmask layer can next be removed from the substrate surface usingknown techniques, for example, a dry-etching process such as reactiveion etching. The resulting structure is a pattern of etched features. Inan alternative exemplary method, it may be desirable to pattern thelayers 102 directly using the resist pattern 104′ without the use of ahardmask layer. Whether direct patterning is employed will depend onfactors such as the materials involved, resist selectivity, resistpattern thickness and pattern dimensions.

The negative tone development methods of the invention are not limitedto the exemplary methods described above. For example, the photoresistovercoat compositions can be used in a negative tone development doubleexposure method for making contact holes. An exemplary such process is avariation of the technique described with reference to FIG. 2, but usingan additional exposure of the photoresist layer in a different patternthan the first exposure. In this process, the photoresist layer isexposed to actinic radiation through a photomask in a first exposurestep. The photomask includes a series of parallel lines forming theopaque regions of the mask. Following the first exposure, a secondexposure of the photoresist layer is conducted through a secondphotomask that includes a series of lines in a direction perpendicularto those of the first photomask. The resulting photoresist layerincludes unexposed regions, once-exposed regions and twice-exposedregions. Following the second exposure, the photoresist layer ispost-exposure baked and developed using a developer as described above.Unexposed regions corresponding to points of intersection of the linesof the two masks are removed, leaving behind the once- and twice-exposedregions of the resist. The resulting structure can next be patterned asdescribed above with reference to FIG. 2.

Further refined resolution for features such as contact holes and trenchpatterns can be achieved using an NTD overexposure process. In thisprocess, the photomask has large patterns relative to those to beprinted on the wafer. Exposure conditions are selected such that lightdiffuses beneath the edge of the photomask pattern causing the polarityswitch in the resist to extend beneath these edge regions.

EXAMPLES Synthesis of Photoresist Polymers (PP)

The following monomers were employed in the synthesis of photoresistpolymers (PP) used in the examples for photoresist compositions;

Synthesis of poly(ECPMA/MCPMA/MNLMA/HADA) (PP-1)

Monomers of ECPMA (5.092 g), MCPMA (10.967 g), MNLMA (15.661 g) and HADA(8.280 g) were dissolved in 60 g of propylene glycol monomethyl etheracetate (PGMEA). The monomer solution was degassed by bubbling withnitrogen for 20 min. PGMEA (27.335 g) was charged into a 500 mLthree-neck flask equipped with a condenser and a mechanical stirrer andwas degassed by bubbling with nitrogen for 20 min. The solvent in thereaction flask was next brought to a temperature of 80° C. V601(dimethyl-2,2-azodiisobutyrate) (0.858 g) was dissolved in 8 g of PGMEAand the initiator solution was degassed by bubbling with nitrogen for 20min. The initiator solution was added to the reaction flask and thenmonomer solution was fed into the reactor dropwise over a 3 hour periodunder rigorous stirring and nitrogen environment. After monomer feedingwas complete, the polymerization mixture was left standing for oneadditional hour at 80° C. After 4 hours polymerization time (3 hoursfeeding and 1 hour post-feeding stirring), the polymerization mixturewas allowed to cool to room temperature. Precipitation was carried outin methyl tert-butyl ether (MTBE) (1634 g). The powder precipitated wascollected by filtration, air-dried overnight, re-dissolved in 120 g oftetrahydrofuran (THF), and re-precipitated into MTBE (1634 g). The finalpolymer was filtered, air-dried overnight and further dried under vacuumat 60° C. for 48 hours to give 31.0 g of poly(ECPMA/MCPMA/MNLMA/HADA)(15/35/30/20) copolymer (PP-1) (Mw=20,120 and Mw/Mn=1.59).

Synthesis of poly(MCPMA/NLM) (PP-2)

Monomers of MCPMA (17.234 g) and NLM (22.766 g) were dissolved in 60 gof PGMEA. The monomer solution was degassed by bubbling with nitrogenfor 20 min. PGMEA (31.938 g) was charged into a 500 mL three-neck flaskequipped with a condenser and a mechanical stirrer and was degassed bybubbling with nitrogen for 20 min. The solvent in the reaction flask wasnext brought to a temperature of 80° C. V601 (2.831 g) was dissolved in8 g of PGMEA and the initiator solution was degassed by bubbling withnitrogen for 20 min. The initiator solution was added to the reactionflask and then monomer solution was fed into the reactor dropwise over a3 hour period under rigorous stirring and nitrogen environment. Aftermonomer feeding was complete, the polymerization mixture was leftstanding for one additional hour at 80° C. After 4 hours polymerizationtime (3 hours feeding and 1 hour post-feeding stirring), thepolymerization mixture was allowed to cool to room temperature.Precipitation was carried out in MTBE (1713 g). The powder precipitatedwas collected by filtration, air-dried overnight, re-dissolved in 120 gof THF, and re-precipitated into MTBE (1713 g). The final polymer wasfiltered, air-dried overnight and further dried under vacuum at 60° C.for 48 hours to give 32 g of poly(MCPMA/NLM) (50/50) copolymer (PP-2)(Mw=8,060 and Mw/Mn=1.46).

Synthesis of Overcoat Polymers (OP)

The following monomers were employed in the synthesis of overcoatpolymers (OP) used in formulating resist overcoat compositions;

Synthesis of Poly(iBMA) (OP-1)

40 g of iso-butyl methacrylate (iBMA) monomers was dissolved in 60 g ofPGMEA. The monomer solution was degassed by bubbling with nitrogen for20 min. PGMEA (32.890 g) was charged into a 500 mL three-neck flaskequipped with a condenser and a mechanical stirrer and was degassed bybubbling with nitrogen for 20 min. The solvent in the reaction flask wasnext brought to a temperature of 80° C. V601 (3.239 g) was dissolved in8 g of PGMEA and the initiator solution was degassed by bubbling withnitrogen for 20 min. The initiator solution was added to the reactionflask and then monomer solution was fed into the reactor dropwise over a3 hour period under rigorous stirring and nitrogen environment. Aftermonomer feeding was complete, the polymerization mixture was leftstanding for one additional hour at 80° C. After 4 hours ofpolymerization time (3 hours feeding and 1 hour post-feeding stirring),the polymerization mixture was allowed to cool to room temperature.Precipitation was carried out in a methanol/water (8/2) mixture (1730g). The precipitated polymer was collected by filtration, air-driedovernight, re-dissolved in 120 g of THF, and re-precipitated in amethanol/water (8/2) mixture (1730 g). The final polymer was filtered,air-dried overnight and further dried under vacuum at 25° C. for 48hours to give 34.2 g of poly(iBMA) polymer (OP-1) (Mw=8,641 andMw/Mn=1.61).

Synthesis of Poly(iBMA/nBMA) (75/25) (OP-2)

30 g of iBMA and 10 g of nBMA monomers were dissolved in 60 g of PGMEA.The monomer solution was degassed by bubbling with nitrogen for 20 min.PGMEA (32.890 g) was charged into a 500 mL three-neck flask equippedwith a condenser and a mechanical stirrer and was degassed by bubblingwith nitrogen for 20 min. The solvent in the reaction flask was nextbrought to a temperature of 80° C. V601 (3.239 g) was dissolved in 8 gof PGMEA and the initiator solution was degassed by bubbling withnitrogen for 20 min. The initiator solution was added into the reactionflask and then monomer solution was fed into the reactor dropwise over a3 hour period under rigorous stirring and nitrogen environment. Aftermonomer feeding was complete, the polymerization mixture was leftstanding for one additional hour at 80° C. After 4 hours ofpolymerization time (3 hours feeding and 1 hour post-feeding stirring),the polymerization mixture was allowed to cool to room temperature.Precipitation was carried out in a methanol/water (8/2) mixture (1730g). The precipitated polymer was collected by filtration, air-driedovernight, re-dissolved in 120 g of THF, and re-precipitated into amethanol/water (8/2) mixture (1730 g). The final polymer was filtered,air-dried overnight and further dried under vacuum at 25° C. for 48hours to give 33.1 g of poly(iBMA/nBMA) (75/25) copolymer (OP-2)(Mw=9,203 and Mw/Mn=1.60).

Synthesis of Poly(iBMA/nBMA) (50/50) (OP-3)

20 g of iBMA and 20 g of nBMA monomers were dissolved in 60 g of PGMEA.The monomer solution was degassed by bubbling with nitrogen for 20 min.PGMEA (32.890 g) was charged into a 500 mL three-neck flask equippedwith a condenser and a mechanical stirrer and was degassed by bubblingwith nitrogen for 20 min. Subsequently the solvent in the reaction flaskwas brought to a temperature of 80° C. V601 (3.239 g) was dissolved in 8g of PGMEA and the initiator solution was degassed by bubbling withnitrogen for 20 min. The initiator solution was added into the reactionflask and then monomer solution was fed into the reactor dropwise overthe 3 hours period under rigorous stirring and nitrogen environment.After monomer feeding was complete, the polymerization mixture was leftstanding for an additional hour at 80° C. After a total of 4 hours ofpolymerization time (3 hours of feeding and 1 hour of post-feedingstirring), the polymerization mixture was allowed to cool down to roomtemperature. Precipitation was carried out in methanol/water (8/2)mixture (1730 g). The precipitated polymer was collected by filtration,air-dried overnight, re-dissolved in 120 g of THF, and re-precipitatedinto methanol/water (8/2) mixture (1730 g). The final polymer wasfiltered, air-dried overnight and further dried under vacuum at 25° C.for 48 hrs to give 32.5 g of poly(iBMA/nBMA) (50/50) copolymer (OP-3)(Mw=8,812 and Mw/Mn=1.60).

Synthesis of Poly(iBMA/nBMA) (25/75) (OP-4)

10 gram of iBMA and 30 gram of nBMA monomers were dissolved in 60 g ofPGMEA. The monomer solution was degassed by bubbling with nitrogen for20 min. PGMEA (32.890 g) was charged into a 500 mL three-neck flaskequipped with a condenser and a mechanical stirrer and was degassed bybubbling with nitrogen for 20 min. Subsequently the solvent in thereaction flask was brought to a temperature of 80° C. V601 (3.239 g) wasdissolved in 8 g of PGMEA and the initiator solution was degassed bybubbling with nitrogen for 20 min. The initiator solution was added intothe reaction flask and then monomer solution was fed into the reactordropwise over the 3 hours period under rigorous stirring and nitrogenenvironment. After monomer feeding was complete, the polymerizationmixture was left standing for an additional hour at 80° C. After a totalof 4 hours of polymerization time (3 hours of feeding and 1 hour ofpost-feeding stirring), the polymerization mixture was allowed to cooldown to room temperature. Precipitation was carried out inmethanol/water (8/2) mixture (1730 g). The precipitated polymer wascollected by filtration, air-dried overnight, re-dissolved in 120 g ofTHF, and re-precipitated into methanol/water (8/2) mixture (1730 g). Thefinal polymer was filtered, air-dried overnight and further dried undervacuum at 25° C. for 48 hrs to give 30.2 g of poly(iBMA/nBMA) (25/75)copolymer (OP-4) (Mw=9,654 and Mw/Mn=1.60).

Synthesis of Poly(nBMA) (OP-5)

40 g of nBMA monomer was dissolved in 60 g of PGMEA. The monomersolution was degassed by bubbling with nitrogen for 20 min. PGMEA(32.890 g) was charged into a 500 mL three-neck flask equipped with acondenser and a mechanical stirrer and was degassed by bubbling withnitrogen for 20 min. The solvent in the reaction flask was next broughtto a temperature of 80° C. V601 (3.239 g) was dissolved in 8 g of PGMEAand the initiator solution was degassed by bubbling with nitrogen for 20min. The initiator solution was added to the reaction flask and thenmonomer solution was fed into the reactor dropwise over the 3 hoursperiod under rigorous stirring and nitrogen environment. After monomerfeeding was complete, the polymerization mixture was left standing forone additional hour at 80° C. After 4 hrs of polymerization time (3hours feeding and 1 hour post-feeding stifling), the polymerizationmixture was allowed to cool to room temperature. Precipitation wascarried out in a methanol/water (8/2) mixture (1730 g). The precipitatedpolymer was collected by filtration, air-dried overnight, re-dissolvedin 120 g of THF, and re-precipitated into methanol/water (8/2) mixture(1730 g). The final polymer was filtered, air-dried overnight andfurther dried under vacuum at 25° C. for 48 hours to give 30.8 g ofpoly(nBMA) polymer (OP-5) (Mw=9,194 and Mw/Mn=1.60).

Synthesis of Poly(nBMA/TFEMA) (50/50) (OP-6)

13.747 g of nBMA monomer and 16.253 gram of trifluoroethyl methacrylate(TFEMA) monomer were dissolved in 45 g of PGMEA. The monomer solutionwas degassed by bubbling with nitrogen for 20 min. PGMEA (23.675 g) wascharged into a 500 mL three-neck flask equipped with a condenser and amechanical stirrer and was degassed by bubbling with nitrogen for 20min. The solvent in the reaction flask was next brought to a temperatureof 80° C. V601 (2.004 g) was dissolved in 6 g of PGMEA and the initiatorsolution was degassed by bubbling with nitrogen for 20 min. Theinitiator solution was added to the reaction flask and then monomersolution was fed into the reactor dropwise over a 3 hour period underrigorous stirring and nitrogen environment. After monomer feeding wascomplete, the polymerization mixture was left standing for oneadditional hour at 80° C. After 4 hours of polymerization time (3 hoursfeeding and 1 hour post-feeding stirring), the polymerization mixturewas allowed to cool to room temperature. Precipitation was carried outin a methanol/water (8/2) mixture (1280 g). The precipitated polymer wascollected by filtration, air-dried overnight, re-dissolved in 90 g ofTHF, and re-precipitated into a methanol/water (8/2) mixture (1280 g).The final polymer was filtered, air-dried overnight and further driedunder vacuum at 25° C. for 48 hours to give 25.5 g of poly(nBMA/TFEMA)(50/50) copolymer (OP-6) (Mw=9,830 and Mw/Mn=1.66).

Synthesis of Poly(TFEMA) (OP-7)

30 gram of TFEMA monomer was dissolved in 45 g of PGMEA. The monomersolution was degassed by bubbling with nitrogen for 20 min. PGMEA(23.314 g) was charged into a 500 mL three-neck flask equipped with acondenser and a mechanical stirrer and was degassed by bubbling withnitrogen for 20 min. The solvent in the reaction flask was next broughtto a temperature of 80° C. V601 (1.849 g) was dissolved in 6 g of PGMEAand the initiator solution was degassed by bubbling with nitrogen for 20min. The initiator solution was added to the reaction flask and thenmonomer solution was fed into the reactor dropwise over a 3 hour periodunder rigorous stirring and nitrogen environment. After monomer feedingwas complete, the polymerization mixture was left standing for oneadditional hour at 80° C. After 4 hours of polymerization time (3 hoursfeeding and 1 hour post-feeding stirring), the polymerization mixturewas allowed to cool to room temperature. Precipitation was carried outin a methanol/water (8/2) mixture (1274 g). The precipitated polymer wascollected by filtration, air-dried overnight, re-dissolved in 90 g ofTHF, and re-precipitated into methanol/water (8/2) mixture (1274 g). Thefinal polymer was filtered, air-dried overnight and further dried undervacuum at 25° C. for 48 hrs to give 22.6 g of poly(TFEMA) polymer (OP-7)(Mw=9,895 and Mw/Mn=1.59).

Synthesis of Overcoat Polymers (OP-8-OP-19)

Additional overcoat polymers were synthesized using similar proceduresas described above for overcoat polymers OP-1-OP-7 using the componentsand amounts specified in Table 1. Weight average molecular weight (Mw)and polydispersity index (Mw/Mn) for the polymers were determined andare set forth in Table 1.

TABLE 1 Composi- Polymer Monomer(s) tion* Initiator** Mw Mw/Mn OP-1 iBMA100 5.0% 8,641 1.61 OP-2 iBMA/nBMA 75/25 5.0% 9,203 1.60 OP-3 iBMA/nBMA50/50 5.0% 8,812 1.60 OP-4 iBMA/nBMA 25/75 5.0% 9,654 1.60 OP-5 nBMA 1005.0% 9,194 1.60 OP-6 nBMA/TFEMA 50/50 4.5% 9,830 1.66 OP-7 TFEMA 1004.5% 9,895 1.59 OP-8 nBMA 100 10.0% 5,625 1.38 OP-9 nBMA 100 2.0% 17,6471.88 OP-10 nBMA 100 1.5% 23,997 1.98 OP-11 iBMA 100 10.0% 5,499 1.37OP-12 iBMA 100 7.0% 6,867 1.55 OP-13 iBMA 100 2.0% 18,913 1.85 OP-14iBMA 100 1.5% 24,087 2.02 OP-15 iBMA/nBMA 50/50 10.0% 5,430 1.42 OP-16iBMA/nBMA 50/50 2.0% 18,455 1.90 OP-17 iBMA/nBMA 50/50 1.5% 22,702 2.04OP-18 iBMA/nBMA/ 60/20/ 4.5% 9,542 1.67 TFEMA 20 OP-19 nBMA/TFEMA 75/254.5% 9,073 1.60 *Molar feed ratio in the polymerization **Mole percentwith respect to monomerPhotoresist Composition PreparationPhotoresist Composition 1 (PC-1)

1.294 g of PP-1 and 1.294 g of PP-2 were dissolved in 29.633 g of PGMEA,19.380 g of cyclohexanone, and 48.450 g of methyl-2-hydroxyisobutyrate.To this mixture was added 0.484 g of “PAG A” described below and 0.029 gof 1-(tert-butoxycarbonyl)-4-hydroxypiperidine. The resulting mixturewas rolled on a mechanical roller for three hours and then filteredthrough a Teflon filter having a 0.2 micron pore size.

Photoresist Composition 2 (PC-2)

1.263 g of PP-1 and 1.263 g of PP-2 were dissolved in 29.620 g of PGMEA,19.385 g of cyclohexanone, and 48.455 g of methyl-2-hydroxyisobutyrate.To this mixture was added 0.484 g of PAG A, 0.029 g of1-(tert-butoxycarbonyl)-4-hydroxypiperidine and 0.062 g of OP-10. Theresulting mixture was rolled on a mechanical roller for three hours andthen filtered through a Teflon filter having a 0.2 micron pore size.

Photoresist Composition 3 (PC-3)

5.061 g of PP-1 was dissolved in 28.140 g of PGMEA, 18.760 g ofcyclohexanone, and 46.900 g of methyl-2-hydroxyisobutyrate. To thismixture was added 0.992 g of PAG A, 0.023 g of1-(tert-butoxycarbonyl)-4-hydroxypiperidine and 0.124 g of OP-10. Theresulting mixture was rolled on a mechanical roller for three hours andthen filtered through a Teflon filter having a 0.2 micron pore size.

Characterization of Overcoat Polymers

A solid solution for each of overcoat polymers OP-1 to OP-19 was made bydissolving the polymer in PGMEA to form a 10 wt % solid solution. Thesolutions were filtered through a Teflon filter having a 0.2 micron poresize. The filtered solutions were coated on 200 mm bare silicon wafers,and the coated wafers were soft-baked at 120° C. for 60 seconds to givea film thickness of about 4000 Å. Two sets of wafers for each polymerwere prepared for dissolution rate and contact angle measurements. Thedissolution rates of overcoat polymers were measured on a dissolutionrate monitor (RDA-800EUV from Litho Tech Japan) using 2-heptanone as adeveloper. Maximum dissolution rates of overcoat polymers werecalculated as an average of 18 dissolution rates acquired through 18different channels.

In order to measure optical properties of overcoat polymers, overcoatpolymer solutions (10% solids by weight in PGMEA) were coated at 1100rpm onto 200 mm bare silicon wafers and soft-baked at 120° C. for 60seconds on a TEL CleanTrack ACT 8 coater/developer to provide a filmthickness of ˜4000 Å. Optical properties of the coated films weremeasure on a VUV-VASE VU-302 ellipsometer (J.A. Woollam Co.).Polarization data was collected at three angles over a wide range ofwavelengths. The generated data was analyzed and fit against a model toobtain n and k values at 193 nm.

Characterization results with overcoat polymers including dissolutionrates in 2-heptanone, water contact angles and optical properties (n andk) at 193 nm are summarized in Table 2.

TABLE 2 Dis- solution Contact angles Poly- rate, Stat- Reced- Advanc-Tilt- mer nm/sec ic ing ing ing n k OP-1 1380 89.2 77.4 88.9 13.5 1.6370.002034 OP-2 2630 89.0 76.3 88.7 14.8 1.649 0.001652 OP-3 5080 88.575.7 89.0 14.8 1.642 0.001958 OP-4 5750 87.9 73.4 90.5 18.2 1.6400.002218 OP-5 6070 87.2 70.5 97.0 29.0 1.646 0.001488 OP-6 2700 95.479.6 96.7 17.7 N/A N/A OP-7 N/A 96.0 84.6 963 13.3 N/A N/A OP-11 218087.5 76.2 90.7 14.9 N/A N/A OP-12 1840 87.6 76.8 92.6 14.8 N/A N/A OP-13600 88.4 76.9 92.6 13.6 N/A N/A OP-14 630 89.0 78.6 90.0 13.0 1.6410.001049 OP-18 1700 93.1 79.3 95.4 16.6 1.620 0.001428 OP-19 5500 93.276.5 92.8 19.3 N/A N/A N/A = Not measuredResist Overcoat Composition Preparation

Resist overcoat compositions were prepared by dissolving an overcoatpolymer and basic quencher (if present) in a solvent using thecomponents and amounts set forth in Table 3. The resulting mixtures wererolled on a mechanical roller for three hours and then filtered througha Teflon filter having a 0.2 micron pore size. The compositions wereformulated based on target thicknesses (after spin coating at 1500 rpm)corresponding to one quarter the wavelength of the incoming wave toreduce reflectance at the overcoat surface.

TABLE 3 Overcoat Target thickness, composition Polymer Quencher SolventÅ OC-1 (Comp) OP-2 (1.560 g) — NBB (98.440 g) 290 OC-2 (Comp) OP-2(4.450 g) — NBB (95.550 g) 880 OC-3 (Comp) OP-2 (1.560 g) — IBIB (98.440g) 290 OC-4 (Comp) OP-2 (4.450 g) — IBIB (95.550 g) 880 OC-5 OP-2 (1.552g) TBOC-4HP (0.008 g) IBIB (98.440 g) 290 OC-6 OP-2 (4.428 g) TBOC-4HP(0.022 g) IBIB (95.550 g) 880 OC-7 OP-2 (3.413 g) TBOC-4HP (0.017 g)IBIB (96.570 g) 880 OC-8 OP-2 (3.396 g) TBOC-4HP (0.034 g) IBIB (96.570g) 880 OC-9 OP-2 (3.361 g) TBOC-4HP (0.069 g) IBIB (96.570 g) 880 OC-10OP-2 (3.396 g) TBPC (0.034 g) IBIB (96.570 g) 880 OC-11 OP-2 (3.396 g)TIPA (0.034 g) IBIB (96.570 g) 880 TBOC-4HP =1-(tert-butoxycarbonyl)-4-hydroxypiperidine, TBPC = tert-butyl1-pyrrolidinecarboxylate, TIPA = triisopropanolamineImmersion Lithographic Process

300 mm silicon wafers were spin-coated with AR™40A antireflectant (Rohmand Haas Electronic Materials) to form a first BARC layer on a TEL CLEANTRAC LITHIUS i+ coater/developer. The wafers were baked for 60 secondsat 215° C., yielding a first BARC film with a thickness of 840 Å. Asecond BARC layer was next coated over the first BARC using AR™124antireflectant (Rohm and Haas Electronic Materials), and was baked at205° C. for 60 seconds to generate a 200 Å top BARC layer. Photoresistcompositions were then coated on the dual BARC-coated wafers andsoft-baked at 90° C. for 60 seconds on a TEL CLEAN TRACK LITHIUS i+coater/developer to provide a resist layer with a thickness of ˜900 Å.Overcoat compositions were coated on top of the resist and soft-baked at90° C. for 60 seconds on a TEL CLEAN TRACK LITHIUS i+ coater/developerto provide an overcoat thickness of 290 or 880 Å.

Negative Tone Development Process

Wafers were exposed through a mask on an ASML TWINSCAN XT:1900iimmersion scanner using a crossed sectoral quadruple (C-Quad)illumination with 1.35 NA, 0.9 outer sigma, 0.7 inner sigma and XYpolarization. The exposed wafers were post-exposure baked at 90° C. for60 seconds and then developed using a 1:1 (by weight) mixture of2-heptanone and n-butyl propionate for 25 seconds on a TEL CLEAN TRACK™LITHIUS™ i+ coater/developer to give negative tone patterns. Optimumenergy (E_(op)) to print 45 nm holes was determined for the singleexposure NTD process by plotting CD values, measured on a Hitachi CG4000CD SEM, as a function of exposure energy using a mask CD at 60 nm (thediameter of an opaque post on the mask) and a pitch CD at 90 nm (a maskCD plus the distance between opaque posts). EL was measured as describedabove for 45 nm contact holes. Local CD uniformity of 45 nm holes wasmeasured as a 3σ of 240 CD values. For each wafer, 20 images were takenper die and 12 contact hole measurements per image were taken at 250Kmagnification. Focus offset was changed in an increment of 50 nm toexamine depth of focus (DOF) for different examples and DOF wasdetermined by the hole fidelity from SEM images taken through the focuschange. The results are shown in Table 4.

TABLE 4 Photoresist Overcoat Overcoat Eop, EL, 3σ CDU, DOF, ExampleComposition Composition Thickness, Å mJ/cm² nm/(mJ/cm²) nm nm  9 (Comp.)PC-2 N/A N/A 44.1 1.41 3.89 100 10 (Comp.) PC-1 OC-3 290 44.9 1.16 3.54100 11 (Comp.) PC-1 OC-4 880 46.1 1.16 3.84 100 12 PC-1 OC-5 290 42.51.28 3.56 150 13 PC-1 OC-6 880 45.9 1.06 3.82 150Improved exposure latitude resulted for Examples 10-13 in which anovercoat layer was used in the lithographic process as compared withExample 9 which did not include an overcoat layer. DOF was significantlyimproved for Examples 12 and 13 employing an overcoat compositioncontaining a basic quencher in accordance with the invention as comparedwith Comparative Example 9, free of an overcoat layer, and Examples10-11 which include an overcoat composition with no basic quencher. Theimproved DOF was observed in the patterns in the form of more contactholes being opened in the defocus areas.Dry Lithographic Process

Dry lithography was performed to examine the effect of different basicquenchers on 200 mm silicon wafers using a TEL CleanTrack ACT 8 linkedto an ASML/1100 scanner. Silicon wafers were spin-coated with AR™77bottom-antireflective coating (BARC) material (Rohm and Haas ElectronicMaterials) and baked for 60 seconds at 205° C. to yield a film thicknessof 840 Å. Photoresist composition PC-3 was coated on the BARC-coatedwafers and soft-baked at 90° C. for 60 seconds on a TEL CleanTrack ACT 8coater/developer to provide a resist layer thickness of 1800 Å. Overcoatcompositions as set forth in Table 5 were coated on top of the resistand soft-baked at 90° C. for 60 seconds on a TEL CleanTrack ACT 8coater/developer to provide an overcoat thickness of 880 Å. The waferswere exposed using an annular illumination condition with 0.75 NA, 0.89outer sigma and 0.64 inner sigma. The exposed wafers were post-exposurebaked at 85° C. for 60 seconds and developed with 50:50 2-heptanone andn-butyl propionate developer for 25 seconds on a TEL CleanTrack ACT 8coater/developer. CD was targeted at 100 nm trenches at 1500 nm pitchusing a mask CD of 100 nm Contact angle, Eop and EL results are setforth in Table 5. As can be seen from this data, similar contact angledata was obtained for different quencher loading and different quenchershaving different polarities. Improved EL was observed with the use of anovercoat.

TABLE 5 Photoresist Overcoat Contact angles Eop, EL, Example CompositionComposition Static Receding Advancing Tilting mJ/cm2 nm/(mJ/cm2) 14(Comp.) PC-3 — 86.1 71.8 90.3 17.7 18.1 9.0 15 PC-3 OC-7 87.2 75.3 91.215.7 19.1 7.4 16 PC-3 OC-8 87.3 75.7 92.2 15.8 19.7 7.3 17 PC-3 OC-987.3 75.5 92.6 16.1 19.3 7.6 18 PC-3  OC-10 87.1 75.2 91.7 16 19.6 8.219 PC-3  OC-11 87.0 76.4 90.7 15.9 19.2 8.1

What is claimed is:
 1. A method of forming an electronic device,comprising: (a) providing a semiconductor substrate comprising one ormore layers to be patterned; (b) forming a photoresist layer over theone or more layers to be patterned; (c) coating a photoresist overcoatcomposition over the photoresist layer, wherein the overcoat compositioncomprises a basic quencher, a polymer and an organic solvent, whereinthe basic quencher forms a graded or segregated layer at the interfacebetween the photoresist layer and photoresist overcoat composition; (d)exposing the layer to actinic radiation; and (e) developing the exposedfilm with an organic solvent developer.
 2. The method of claim 1,wherein the organic solvent developer comprises 2-heptanone.
 3. Themethod of claim 1, wherein the organic solvent developer comprisesn-butyl acetate.
 4. The method of claim 1, wherein the organic solventdeveloper comprises n-butyl propionate.
 5. The method of claim 1,wherein the organic solvent of the photoresist overcoat compositioncomprises an alkyl butyrate.
 6. The method of claim 5, wherein theorganic solvent of the photoresist overcoat composition comprises aC₈-C₉ alkyl butyrate.
 7. The method of claim 1, wherein the organicsolvent of the photoresist overcoat composition comprises an alkylpropionate.
 8. The method of claim 7, wherein the organic solvent of thephotoresist overcoat composition comprises a C₈-C₉ alkyl propionate. 9.The method of claim 1, wherein the organic solvent of the photoresistovercoat composition comprises a ketone.
 10. The method of claim 9,wherein the solvent comprises a C₈-C₉ branched ketone.
 11. A method offorming an electronic device, comprising: (a) providing a semiconductorsubstrate comprising one or more layers to be patterned; (b) forming aphotoresist layer over the one or more layers to be patterned; (c)coating a photoresist overcoat composition over the photoresist layer,wherein the overcoat composition comprises a basic quencher, a polymerand an organic solvent, wherein the basic quencher has a high surfacefree energy relative to other components of the overcoat composition;(d) exposing the layer to actinic radiation; and (e) developing theexposed film with an organic solvent developer.